Conventionally, as described, for example, in Japanese Laid-open Patent Publication Hei 10-290028, a device for color-mixing light from single-color LEDs such as red, blue and green without color unevenness is known, in which all the light emitted from the LEDs is projected on a reflector for multiple reflection so as to extract only indirect light, thereby improving the color mixing properties of light. Further, as described, for example, in Japanese Laid-open Patent Publication 2002-133932, a device is proposed, in which a light guide member and a diffusion layer are added so as to emit light from each LED in one direction by using the total reflection of the light guide member, and to uniformly increase the scattering properties by using the diffusion layer, thereby improving the color mixing properties of the emitted lights.
However, in the color mixing using reflected light as described above, the amount of emitted light decreases as the number of reflections increases due to absorption by the reflecting surface, although the increase in the number of reflections improves the color mixing properties. Further, the emitted light is scattered at various angles, resulting in a wide-angle light distribution. Besides, if the diffusion layer is made of fine particles or the like, the diffusion properties are improved with their concentration, which however reduces transmittance. Further, the emitted light is scattered at various angles, resulting in a wide-angle light distribution.
Further, as described, for example, in Japanese Laid-open Patent Publication Sho 60-130001, a condenser lens formed by combining a convex incident surface and a total reflection surface is proposed to change the wide-angle light distribution of an LED element to narrow-angle light distribution so as to increase intensity. The condenser lens has two kinds of light paths: a light path to allow the incident light on the lens from the centrally placed LED element to be emitted as substantially parallel light relative to the lens center axis (optical axis) based on the total reflection by the reflecting surface; and a light path to allow the incident light to be collected and emitted as substantially parallel light relative to the optical axis based on the refraction by the convex incident surface. A light source unit of narrow-angle light distribution to emit substantially parallel light relative to the optical axis is achieved by the both light paths. In the case of using one LED element, the central placement of the LED element allows the light emitted from the LED element to be refracted by the convex incident surface and to be emitted as substantially parallel light which is symmetrical relative to the lens center axis.
However, if multiple LED elements are used, it is not possible to centrally place one LED element. Thus, if multiple single-color LED elements are used for the condenser lens, the positions of the LED elements of multiple light colors are offset on one side, respectively, relative to the lens center axis, so that paths of light emitted from the respective LED elements and passing through the convex incident surface are asymmetrical relative to the lens center axis, causing color unevenness. Further, even if the convex incident surface is flat, such axial asymmetry remains, causing color unevenness.